Progress in nuclear cardiology: new imaging beyond perfusion and function

The rapid development of nuclear medicine instruments and the widespread availability of new radiopharmaceutical agents has created a new era of nuclear cardiology. This review will introduce new techniques beyond perfusion and function that have recently become available in Japan. Tc-99m perfusion imaging agents provide excellent myocardial perfusion images that may enhance diagnostic accuracy in the study of coronary artery disease. In addition, greater photon flux from the tracer permits simultaneous assessment of regional perfusion and function with the use of first-pass angiography or ECG-gated acquisition. In addition, Tc-99m perfusion agents are available for acute patients in emergency departments. When the tracer is administrated at both the acute and subacute phases of myocardial infarction, perfusion SPECT imaging permits accurate estimates of areas at risk and salvaged myocardium. Nuclear cardiology has progressed toward biochemical imaging in vivo. Positron emission tomography (PET) enables metabolic assessment in vivo. Preserved FDG uptake indicates ischemic but viable myocardium that is likely to improve regional dysfunction after revascularization. While FDG-PET is available only in a limited number of facilities, FDG-SPECT using ultrahigh energy collimators and branched fatty acid analog I-123 BMIPP SPECT offer potential for metabolic imaging in routine clinical settings. Less uptake of BMIPP than thallium is often observed in the ischemic myocardium and hypertrophic cardiomyopathy. Such a perfusion-metabolic mismatch as that in FDG-PET seems to be similarly observed in BMIPP SPECT. Severe ischemia is identified as reduced BMIPP uptake at rest despite normal or normalized perfusion, suggesting a significant role of BMIPP in ischemic memory imaging. I-123 MIBG uptake in the myocardium reflects adrenergic neuronal function in vivo. In the study of coronary artery disease, neuronal denervation is often observed around the infarcted myocardium and post-ischemic region as well. More importantly, reduced MIBG uptake in these patients can assess the severity of congestive heart failure. In addition, the improvement in MIBG can be seen in relation to improved patient condition following medical treatment. These new techniques will provide insights into new pathological states in ischemic heart disease and a variety of myocardial disorders. Nuclear cardiology plays an important role in selecting optimal treatments for these patients.